Trial Frame Slots Explained Simply | Generated by AI
Good question — this is about the trial frame design itself, not the PD numbers.
Three Insertion Slots
- A trial frame with three insertion slots per eye means each eye can hold up to three lenses at the same time.
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For example, the optician might insert:
- A spherical lens (basic myopia or hyperopia correction)
- A cylindrical lens (astigmatism correction)
- A prism lens (if needed, or an additional test lens such as progressive trial lens)
- This allows the optician to simulate your full prescription without needing to grind a custom lens first.
Four Insertion Slots
- Yes, four-slot trial frames exist (less common, but available in professional optometry sets).
- They give more flexibility, such as adding a tinted filter, polarizer, or progressive test lens in addition to the regular correction lenses.
- They’re bulkier and heavier, so usually used in clinics rather than for simple home testing.
How to Choose
- Three-slot trial frames are standard and enough for almost all testing.
- If you only want to try progressive lenses for comfort and corridor fit, three slots are completely sufficient.
- Four-slot frames are mostly useful for professional optometrists who need to layer extra test lenses.
👉 For personal or “try-before-you-buy” progressive lens use, I’d recommend three-slot adjustable PD frames (lighter, cheaper, easier). Four-slot is overkill unless you’re setting up a small optometry lab.
Would you like me to list the typical product names/keywords for three-slot vs four-slot frames (like how they appear on Amazon or optical supply sites)?